25010

Check Encoder Reference Signal

Navigate to Diagnostics > Drive > Encoder and monitor the reference mark signal (R signal) while manually moving the axis through the expected reference position.

Use oscilloscope on encoder R+ and R- terminals to verify 11µApp signal amplitude

Verify Encoder Power Supply

Check encoder supply voltage at terminals 467/468 on drive unit - should be 5VDC ±5% for incremental encoders or 8-30VDC for absolute encoders.

Disconnect drive power before measuring encoder supply voltages

Inspect Encoder Mechanical Condition

Remove encoder cover and inspect code disk for cracks, contamination, or misalignment. Clean with lint-free cloth and isopropyl alcohol if contaminated.

Look for oil film on glass disk - common cause of intermittent reference mark detection

Verify Reference Search Distance

Check MD34060[axis] REFP_SEARCH_DIST in Commissioning > Machine Data. Ensure value exceeds the maximum distance between reference point and encoder zero mark.

Set REFP_SEARCH_DIST to 1.5x the actual required search distance for safety margin

Check Reference Point Direction

Verify MD34040[axis] REFP_SEARCH_DIR matches the physical direction needed to reach the encoder reference mark from the approach position.

Incorrect search direction can cause collision with mechanical limits

Validate Reference Point Velocity

Check MD34020[axis] REFP_VELO_SEARCH_MARKER is appropriate for encoder type - typically 50-200 mm/min for glass scale encoders to ensure reliable mark detection.

Check Encoder Cable Continuity

Measure resistance between encoder connector and drive terminals for R+/R- signals (typically pins 6/7). Should show <5 ohms resistance and >1M ohm isolation.

Power down drive completely before disconnecting encoder cables

Verify Drive Encoder Interface

Access Diagnostics > Drive > Status and check encoder interface status bits. Look for 'Encoder supply fault' or 'Reference mark error' indicators.

S120 drives show encoder status in r0482 - bit 0 indicates reference mark validity

Test with Known Good Encoder Cable

Temporarily replace encoder cable with verified working spare to isolate cable-related issues. Ensure proper cable type (motor/encoder specific) and maximum length limits.

Check Reference Point Switch Operation

Navigate to Diagnostics > PLC > Inputs and verify reference point switch signal (typically DB31.DBX1.0 for X-axis) activates at correct mechanical position.

Reference switch should activate 2-5mm before encoder zero mark position for proper approach

Verify Mechanical Travel Limits

Ensure software limits MD36100[axis] SOFT_LIMIT_MINUS and MD36110[axis] SOFT_LIMIT_PLUS allow sufficient travel to reach encoder reference mark.

Disable software limits only temporarily and under careful supervision

Check for Mechanical Obstructions

Manually verify axis can travel to reference position without binding, collision, or excessive force. Check for chip buildup, damaged way covers, or misaligned components.

Inspect Encoder Mounting

Check encoder mounting bolts for proper torque and verify no movement between encoder housing and machine structure during axis motion.

Use dial indicator on encoder housing while moving axis to detect mounting looseness

Check Encoder Coupling Condition

Inspect flexible coupling between encoder and axis for wear, cracking, or excessive backlash. Replace if any damage is visible.

Support encoder weight when disconnecting coupling to prevent shaft damage

Verify Encoder Shaft Alignment

Check encoder shaft alignment using dial indicator - maximum 0.1mm radial runout and 0.05mm axial play are typically acceptable limits.